1986 Fiscal Year Final Research Report Summary
A Study for Leak Before Break Theory in Pressure Vessel and Pipings
| Project/Area Number |
60420047
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
溶接工学
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| Research Institution | Yokohama National University |
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Principal Investigator |
OGURA Nobukazu Yokohama National University , Professor, 工学部物質工学科, 教授 (10017949)
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| Co-Investigator(Kenkyū-buntansha) |
SAKAI Yuzuru Yokohama National University , Assistant, 工学部物質工学科, 助手 (90114975)
ANDO Kotoji Yokohama National University , Associate Professor, 工学部物質工学科, 助教授 (40017992)
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| Project Period (FY) |
1985 – 1986
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| Keywords | Strength of Material / Fracture Mechanics / Pressure Vessel / Leak Before Break / LBB |
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| Research Abstract |
In order to investigate the L.B.B. conditions of pressure vessles and pipings, basic experiments were made using large scale flat specimens. A material used was a STS-42 steel, and rectangular specimens with central surface notches were tested using a tensile machine produced in this study. Monotonic or cyclic loads which was a slightly lower than the maximum load in monotonic condition, were loaded on a specimen, and load-displacement curve was recorded with a high-frequency data recorder. From this study, the following results were obtained;
(1) In a monotonic loading condition, a load increased up to a maximum load and then decreased to be constant for a while. The levels of plateaus varied with the sizes of the initial flaws, however, the values were within 80 to 90% of each maximum value. In a cyclic loading, L.B.B. condition was observed when a load slightly lower than the constant value appeared in a monotonic test was loaded.
(2) In cyclic load tests, large deformations were observed at the back surface of specimens. Therefore, it will be possible to repair the components of a pressurized structure by detecting the deformations with a monitering devise before the catastrophic failure occurres.
(3) From fracture appearance of specimens, the following fact was clarified. In a cyclic load test, a crack appeared in a back surface of a specimen grew with a high velocity for a while, then the crack velocity decreased till the crack length became almost equal to the length of a crack at front surface. After the instant, the crack grew rapidly and the specimen was broken.
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